Maggie Gondeck
Great Ideas Science
Research Paper
Should Factories Filter Their Smoke Emissions?
Should coal fired power plants be responsible for recovering the emissions that their
smoke stacks emit? Coal burning power plants are the largest source of mercury emissions
related to human activity in the United States. Almost all of the electricity that powers modern
life comes from burning fossil fuels like coal, natural gas, and oil. Acid deposition is caused by
two pollutants that are released into the atmosphere, or emitted, when these fuels are burned:
sulfur dioxide and nitrogen oxides. Toxic air pollutants, or air toxics, are known to cause or are
suspected of causing cancer, birth defects, reproduction problems, or other serious illnesses.
Exposure to certain toxic pollutants can even cause death.
Coal accounts for most of the United States sulfur dioxide emissions and a large portion
of nitrogen oxide emissions. Sulfur is present in coal as an impurity, and it reacts with air when
the coal is burned to form the sulfur dioxide. In contrast, nitrogen oxide is formed when any
fossil fuel is burned.
Acid deposition penetrates deeply into the fabric of an ecosystem, changing the chemistry
of the streams and narrowing, sometimes to nothing, the space where certain plants and animals
can survive. Because there are so many changes, it takes many years for ecosystems to recover
from acid deposition, even after emissions are reduced and the rain becomes normal again. For
example, while the visibility might improve within days, and small or episodic chemical changes
in streams improve within months, chronically acidified lakes, streams, forests, and soils can
take years to decades or even centuries to heal.
As emissions from the largest known sources of acid deposition, power plants and
automobiles, are reduced, EPA scientists and their colleagues must assess the reductions to make
sure they are achieving the results that Congress had anticipated. If these assessments show that
acid deposition is still harming the environment, Congress may begin to consider additional ways
to reduce emissions that cause acid deposition. They may consider additional emissions
reductions from sources that have already been controlled, or methods that have already been
controlled, or methods to reduce emissions from other sources. They may also invest in energy
efficiency and alternative energy. The cutting edge of protecting the environment from acid
deposition will continue to develop and implement cost effective mechanisms to reduce their
impact on the environment.
For now, it is much more economically efficient to capture the carbon dioxide that enters
the atmosphere from the smokestacks of large centralized sources such as power plants, cement
plants, fertilizer plants, and refineries.
Indeed the researchers say the cost of removing carbon dioxide directly from the air would be so
large that paying for it would require the equivalent of a ten dollar per gallon tax on gasoline.
The cost estimates are similar to those presented earlier this year in a study that had been done
earlier.
Given the known health hazards from factory smokestack emissions, particularly those of
coal-burning electric power plants, it is highly desirable to reduce the emissions at their source.
One proven way of doing this is to install scrubbers in the emission system. The technology of
scrubbers, which can remove a very large proportion of the sulfur dioxide from smokestack
emissions, is constantly being refined.
The technology of scrubbers, which can remove a very large portion of the sulfur dioxide
from smokestack emissions, is constantly being refined. While one might imagine that scrubbers
would be installed directly inside a smokestack, they can in fact be added at many points around
it. Some scrubber installations require the addition of an entire building or complex to a coal
plant. When soft coal or oil are ignited and burned, sulfur dioxide is produced. The main method
of removing sulfur dioxide from emissions is to put the flue gas from industrial plants through a
tank containing a sprayed mixture of powdered limestone and water. The resulting chemical
reaction produces a synthetic form of the mineral gypsum, which can be adapted for the use of
concrete or drywall. This can be done in a few different ways. In a wet scrubber, the untreated
exhaust is sent through a spray chamber where fine water droplets knock down harmful
particulates. The water at the bottom of the chamber enters a miniature water treatment plant
where the sediments are removed before the water is recycled to be used again. Dry scrubbers
use a granulated solid material or electrostatic technology to intercept the particulates, creating a
dry waste product. These are not as common as wet scrubbers because of their higher costs of
installation. In either case, before the flue gas reaches the scrubber reaches the scrubber, it may
first pass through a filter that consists of some type of cloth bag to catch large particles. A second
filter may be installed to catch very small particles after the flue gas leaves the scrubber.
Before the 1990 Clean Air Act Amendments, the EPA regulated air toxics one chemical
at a time. This approach did not work well. Between 1970 and 1990, the EPA established
regulations for only seven pollutants. The 1990 Clean Air Act Amendments took a completely
different approach to reducing toxic air pollutants. The Amendments required the EPA to
identify categories of industrial sources for 187 listed toxic air pollutants and to take steps to
reduce pollution by requiring sources to install controls or change production processes. It makes
good sense to regulate by categories of industries rather than one pollutant at a time, since many
individual sources release more than one toxic chemical. Developing controls and process
changes for industrial source categories can result in major reductions in releases of multiple
pollutants at one time.
The EPA has published regulations covering a wide range of industrial categories,
including chemical plants, incinerators, dry cleaners, and manufacturers of wood furniture.
Harmful air toxics from large industrial sources, such as chemical plants, petroleum refineries,
and paper mills, have been reduced to nearly 70 percent. These regulations mostly apply to large,
or so called major sources, and also to some smaller sources known as area sources. In most
cases, the EPA does not prescribe a specific control technology, but sets a performance level
based on a technology or other practices already used by the better controlled and lower emitting
sources in an industry. The EPA works to develop regulations that give companies as much
flexibility as possible in deciding how they reduce their toxic air emissions, as long as the
companies meet the levels required in the regulations.
The 1990 Clean Air Act required the EPA to set regulations using a technology based or
performance based approach to reduce toxic emissions from industrial sources. After the EPA
sets the technology based regulations, the Act requires the EPA to evaluate any remaining risks,
and decide whether it is necessary to control the source further. That assessment of remaining
risk was initiated in the year 2000 for some of the industries covered by the technology based
standards.
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